Evapotranspiration from wheat under a semi-arid climate and a shallow water table

Abstract

Field experiments were conducted to study crop evapotranspiration and its relationship with Class A Pan evaporation for wheat cultivars WH-283 and WH-2009 grown in a semi-arid climate in sandy loam soils with shallow ground water table. The irrigation treatments were wet, middle and dry. The values of soil moisture at different soil depths, seasonal soil moisture depletion in crop root zone, and capillary contribution from ground water to crop root zone were different for different treatments and were influenced by rainfall pattern, irrigation, ground water table depth, and plant factors. The capillary contribution was lower under the dry treatment as compared to the wet treatment due to restricted plant growth and lesser capability of plants to extract water under dry treatment. The cumulative evapotranspiration increased at a decreasing rate with time from sowing to harvesting and the values were higher for wheat cultivar WH-283 as compared to cultivar WH-2009. The seasonal evapotranspiration varied from 163.6 to 382.6 mm for different treatments. The ratio of actual evapotranspiration to Class A Pan evaporation ( E a E pan ) for different crop growth stages increased from 0.1 at germination to the maximum value and then decreased towards the crop ripening. The maximum values of the E a E pan ratio varied from 0.61 to 1.8 for different treatments and occurred earlier for the wet as compared to the dry treatments. The values of the ratio and the actual evapotranspiration for different wheat cultivars were influenced by rainfall pattern, irrigation, ground water table depth, and soil and plant factors in addition to Class A Pan evaporation. Therefore, the values of the E a E pan ratio can not be generalized for a particular agro-climate and should be used with caution in irrigation planning.